A gas generator used to expand and inflate the airbag rapidly so as to protect a vehicle occupant from the shock at a car collision is built in an airbag module secured in a steering wheel or an instrument panel. The gas generator operates to ignite an igniter device (squib) under control of electrical signals from a control unit (controller) to burn enhancer agent (enhancer) and then burn gas generant by the flames of the enhancer agent, thereby generating a large amount of gas rapidly.
A so-called, double-cylinder type gas generator having a central space, equivalent to an ignition chamber of the gas generant, and an annular space, equivalent to a combustion/filtering chamber, formed at the outside of the central space concentrically, for burning and cooling gas and collecting slag is known as a conventional gas generator.
This type of gas generator is disclosed, for example, by JP Laid-open (Unexamined) Patent Publication No. Hei 9-207705. As shown in FIG. 8, this gas generator has a housing formed in such a manner that a central space of a housing structure, serving as the ignition chamber, is formed by an upper casing 51 of a double-cylinder structure and a lower casing 54 of a double-short-cylinder structure being butt-welded by friction welding, first, and, then, an annular space, serving as the combustion/filtering chamber, is formed around the central space. A squib 68 and enhancer agents 69 are housed and contained in the ignition chamber P from below. On the other hand, a ring-shaped cover member 66 having a cross section of a double-flanged concave form is fixedly placed in the combustion/filtering chamber F, with its flanges 66d, 66e abutted with flashes 52b, 53b of the upper casing 51. Gas generant 57 and a cooling/slag collecting member 60 are contained in sequence in the annular space defined between the cover member 66 and the upper casing 51 so that they are arranged in a radial direction thereof. The combustion/filtering chamber F is formed in this manner. Ring-shaped cushioning members 58, 59 are provided at upper and lower sides of a layer of the gas generant 57, respectively. Also, seal members 61, 62 are provided at upper and lower sides of the cooling/slag collecting member 60, respectively. Further, an aluminum foil 64 to close a gas discharge orifice 53a and an aluminum foil 65 to close an enhancer orifice 52a are adhesively bonded. With this construction, the gas generator that can sufficiently withstand an increased inner pressure by the gas generated in a gas generation chamber G can be obtained.
However, this double-cylinder type gas generator requires an increased number of components of the gas generator and also requires a complicated structure, as shown in FIG. 8. Due to this, there are limits for this type of gas generator to cut the production cost while maintaining the safety of the gas generator. Further, this type of gas generator has a small capacity to hold the gas generant. Due to this, it is mainly applied to a driver's side airbag system and is never applicable to a passenger's seat airbag system requiring a large amount of generated gas.
For example the gas generator shown in FIG. 9 is known as the gas generator for an automobile passenger's seat airbag system. As shown in FIG. 9, the conventional gas generator for the passenger's seat airbag system has a housing 80 comprising an outer cylinder 81 having a plurality of gas discharge holes 81a and a cover member 82 friction-welded to an end of an aperture of the outer cylinder 81. An inner cylinder 85 is inserted and placed in the housing 80. The inner cylinder 85 has gas penetrating holes 85a, containing a prescribed amount of gas generant 86 in an interior thereof. A cylindrical burst plate 83 to close the gas discharge holes 81a formed in the outer cylinder 81 and a cylindrical filter member 84 are disposed in an annular space between the inner and outer cylinders. The cylindrical filter member 84 is packed in the annular space as tight as possible, leaving no space therein, for the purpose of reduction in diameter of the housing 80. Also, an igniter device 89 comprising an igniter 87 that ignites at the detection of collision by collision sensors and enhancer agent 88 ignited by the igniter 87 is disposed in the cover member 82.
This conventional gas generator for the passenger's seat airbag system has a cylindrical shape, as described above, and is built in the airbag module secured in an interior of the instrument panel of the automobile, with its body oriented horizontally along the instrument panel and both lengthwise ends thereof fixed therein. Due to this, a large occupied area is required for placement in the instrument panel. Also, the way of and the structure for assembling the gas generator in the airbag module are complicated, thus involving troublesome works.
Also, owing to the cylindrical shape, it is difficult to pack the gas generant 86 in the interior of the housing with high packing efficiency. Obtaining an equal amount of generated gas to conventional, while fulfilling the recent demands for reduction in size and weight of the gas generator, requires the use of gas generant that can generate more amount of gas. Doing so requires the housing capable of well withstanding the high pressure at the generation of gas.
It is an object of the present invention to provide a gas generator that can provide a simplified structure of the gas generator and also can exhibit good gas generation performances of generating a large amount of gas, while maintaining high safety, even when reduced in size and weight.